Field of the Invention
The present invention relates to image quality adjustment control of an image forming apparatus.
Description of the Related Art
An image forming apparatus of an electrophotographic method forms an electrostatic latent image on a photosensitive member based on input image data, develops the electrostatic latent image using a developer, and forms, on a sheet, the image on the photosensitive member. Then, the image forming apparatus conveys, to a fixing device, the sheet on which the image is formed, and the fixing device fixes the image onto the sheet by applying heat and pressure.
At this time, in order to form an image having a target density on a sheet, the image forming apparatus performs image quality adjustment control. An image forming apparatus discussed in U.S. Pat. No. 7,509,065 fixes measurement images formed on a sheet to the sheet, then measures the measurement images on the sheet using a sensor, and adjusts image forming conditions based on the measurement results.
This image forming apparatus forms, on the sheet, reference images different from the measurement images, and based on the results of the sensor detecting the reference images, determines the timing when the measurement images on the sheet reach the measurement position of the sensor. Through this operation, even if the timing when the sheet enters the measurement position of the sensor shifts, the image forming apparatus prevents the sensor from erroneously detecting the measurement images.
Incidentally, the image quality adjustment control includes maximum density adjustment control for controlling a maximum density to be a target maximum density, and gradation adjustment control for controlling the gradation characteristics of the image forming apparatus to be ideal gradation characteristics. In the image quality adjustment control, first, the maximum density adjustment is executed to determine image forming conditions for forming an image having the target maximum density. Then, the gradation adjustment control is executed.
However, the amount of developer of the reference images developed in the maximum density adjustment control may be so large that the fixing device cannot completely fix the reference images onto the sheet. This is because the amount of developer to be attached to the electrostatic latent image changes due to environment conditions such as temperature and humidity, and the amount of charge of the developer.
If the fixing device cannot completely fix the developer of the reference images, part of the developer of the reference images is not fixed to the sheet and comes off. As a result, the sensor may not be able to detect the reference images, and it may not be possible to determine with high accuracy the timing when the measurement images on the sheet reach the measurement position of the sensor.